Briquetting press

ABSTRACT

A roll-type press for compressing particulate metal powders, especially ferrous metal powders such as produced in direct iron ore reduction processes, to provide series, or strings, of readily separable briquettes as articles of manufacture. The mold pockets in the faces of the two cooperating rolls are so arranged that they partially overlap as the pockets of one roll come into contact with the pockets of the other. The overlapping section, or junctures, of the compacted briquettes are less densely compacted than those conventionally produced so that the individual briquettes of the issuing series can be readily broken apart. Moreover, forces are generated which aid in the release of the briquettes from the mold pockets.

United States Patent [III Assistant Examiner-Lucius R. Frye Anorneys-Manahan and Wright and Llwewllyn A. Proctor ABSTRACT: A roll-type press for compressing particulate metal powders, especially ferrous metal powders such as produced in direct iron ore reduction processes, to provide series, or strings, of readily separable briquettes as articles of manufacture. The mold pockets in the faces of the two cooperating rolls are so arranged that they partially overlap as the pockets of one roll come into contact with the pockets of the other. The overlapping section, or junctures, of the compacted briquettes are less densely compacted than those conventionally produced so that the individual briquettes of the issuing series can be readily broken apart. Moreover, forces are generated which aid in the release of the briquettes from the mold pockets.

PATENTfinJuLzmsn 3,593,37

SHEET 1 BF 2 FIG. 2.

INVENTOR. WILLIAM J. METRAILER ATTORNEY PATENTEUJULZOIQTI 3.593378 SHEET 2 [W2 BRIQUETTING' PRESS Roll press briquettingof particulate metal powders, especially ferrousmetal powders such: as produced in direct iron.

ore reduction processes, has been long. knownto the art. Briquettes arethus formedby withdrawingparticulateor.fine ly divided reduced iron products from direct reduction processes and'feedingsame, generally while.hot,.into"ahopper provided with ascrew-type device-forconveying theproduct.

into the nip of the pair,of press,=rolls-,=atleastoneof whichcontains mold pockets sothat theparticulate iron is-compacted:

therein into briquettes.

Briquettes are generally cast'. so. that the cross sections thereof. resemble Ds" or pillows (D's, back-to-back')..lnbriquetting the particulate reduced iron product of direct reduction processes,,despite the ,normally highervproduction:

achieved by casting pillow-shapedbriquettes, it is-often necessary or desirable to cast. the briquettes as Ds to achieve the necessary high density required to provide low porositystructures. Low porosity structuresarenecessary becausethislessens moisture pickupand reoxidation, which isso acute in loosely packed agglomerated metals, especially activemetals such as produced in a direct'ircn orereductionprocess. Thus,

with any givenpress, at similar conditions, Dshaped briquetteswill be of greater density.,.and hence. more impervious to moisture pickup and reoxidation than pillow-shaped briquettes.

For practical operation with'conventional presses, iristhe joined briquettes wherein theyparticulate: metal .ismore tightly'compacted, or hasa much. greaterdensity, than other portions of the briquettes. Ideally, the .webbed sectionsshould provide a juncture for easy separation of the briquettes, 'one fromanother. Unfortunately, however, this is not the case in briquetting many particulate metals, especially particulate reduced iron. Extreme. pressures are.required: to produce the' necessary high density agglomeration: of theumetal..The.high;

pressure on the rolls at the webbed sections of the. briquettes produces considerable wear. Binders, whichnormallyreduce the need for the very high. pressures, cannot be employed. A

principal reason for this is that the-binder'material provides an undesirable contaminant, and hence interferes with the processes in which the briquettes are to be used. Con

sequently, separation of the briquettes from individual series.-

constitutes a troublesome problem.

A string breaker, i.e., deviceconstituted of a pairof'sloped surfaces, is generally mounted. immediately-'belowthezrolls to intercept the series of briquettes, and-skew it from its path to twist and tear the webs to separate theindividual briquettes.

String breakers functionfairly satisfactorily when the -firstv briquettes of .anlunbroken series'is-properly intercepted; Un-. fortunately, the first briquetteof a series, particularly"-D-.. shapes, frequentlydonot release cleanly from the:pockets.and.

is notproperly intercepted. The malfunction locks:or;retains the'briquette in a'moldpocket and:the-protruding-.portion.of the briquette :strikes the. string .breaker. Repeated blows damage the rolls.

promote .briquette release. Unfortunately, however, lubricants reduce the roll grab necessary to ensure adequate feed rate.

Thus, lubricity at thepowder compact interfaceand within-the powder .are important features.- On.,the one.hand,-minimum compacted. 0n the other hand, maximum friction between rollsandpowdersis required to ensure suitable feedingror-grab bywthexpair of rolls. Hence, the amount of lubricant whichcan be employedislimited. The useof shallowpockets also aids in release. This however, lowers the production capacityof'the presses and, obviously, isgenerally undesirable;

Itisaaccordingly the primary object of the present invention to:obviate1these and other'difficulties. In'particular, it is anobject. to provide a new and improved roll-type" press for briquettinggparticulate metals, especially ferrous metals such astresultant fromdirect iron ore reduction processes. More particularly, itis'an'object to provide a press which gives'improved roll life' and superiorperformance, as well-asone which isuseful-in high-temperature briquetting of products fromdirect' iron orereductionprocesses, especially fluidized iron 'ore reduction processes.

These .andother objects are achievedin accordance with thepresent invention which contemplates-a new and improved roll-type presswhereinthe rolls have mold pockets inalternate sides of the'roll facings so that the pockets-of one roll partially overlap the pockets of the other. Particulate metal powder introduced into the pockets is compressed as the' pocketsare rotated into contacttoprovide series-orstringsof 'briquettes, as-articles of manufacture, while the" overlapping sections provide junctures in the briquettes which ar'eareas of less. dense compaction than achievedinconventional operations,:supra..The individual briquettes of the issuing series, or

strings, .as aresult are more readily broken apart, one "briquette from another; Moreover, forces are generated which aid inthereleaseof the briquettes from themold pockets.

This improvement greatly reduces oneof the major'factors of: roll damage, i.e., that caused during the separation or breaking apartof the individual briquettes of a series. "it also 'aidsintheseparation, and the tendency of briquettes to stick inthemold pockets :is also alleviated. Thus, the normal-tendency of briquettes to stick'withinthe moldpocket of one face of a roll is largelyoffset'by the slight pulling efiect of the next briquetteofthe series, which is'in-a 'mold pocket of the op 'posite'rolltherebyexisting'a tendency to'foliow in the path of the. movingroll.

Partial overlap is provided between the'alterna'ting series-of mold pockets. It has 'been found desirable to provide overlap rangingfromabout l to about 20 percent, and-preferably fro'm' about'S to-about 15 percent, based on the sum total length of overlapped and nonoverlapped sections. The overlapped edges. of the-individual briquettes in an issuing series of The invention willbe'better understood by reference to the following-detaileddescription which makes'further reference to the drawings which are partial section, or fragmentary,

views illustrating-the salient and necessary features.

In-the drawings:.

.FIGw'l depicts,'in section, a general assembly side viewo'f a press' with 'afeed hopper-mounted t-hereabove (string breaker not shown),

H63 2, which is a view along 2-2 of FIG. 1, depicts in plan a 65 ,pairof'cooperating press rolls, deform the stringbreakers to the extent that they-:ruband desired to ensure thenecessary. flow; of the powder as it is FIGS depicts an enlarged portion of the press rolls of FIG. 1, and a.series,-orstring, of briquettes of D-shaped cross sec tion, as would issue from a press such as described by reference to the-preceding figures, and

FIG. 4 depicts a preferred roll design.

Referringto the figuresJhere is shown'a roll-type press 10 provided with a pair of cooperating-rolls 11,12. One face *of'a rollis' in operative proximity with theother, andeach roll'is mounted for rotation in opposite directions about its respective axis,-'A,A. The drive shaft 13,-suitably coupled to a convenient power source (not shown), drives shafts 14,15 via suitable gear means 16.

A hopper 20, containing a vertically oriented drive shaft 21, forces particulate metal powder from the hopper into the nip, or grab, of the pair of rolls 11,12. Therein compression of the powder is initiated. The vertical shaft 21 is driven by any suitable motor, or motorand drive-transmitting means (not shown).

The circumference of the pair of rolls 11,12 is provided with a continuous series of mold segments containing pockets (or voids) 21,22viz., 21, to 21, and 22, to 22 the subscript n representing any predetermined desired whole number of mold segment required to align the circumference of a roll. The mold segments per se, of course, are utilized so that after excessive wear the molds can be changed without the necessity of changing a whole roll. While in this instance the transverse distance (length) of a pocket 21,22 is shown as lesser than the longitudinal distance (width) of a pocket 21,22, the opposite could as well be true, or both distances could be equal. n the other hand, while only a single pocket 21,22 is aligned in the transverse direction on a roll, a plurality thereof could be so aligned without changing the nature of the present invention. It, of course, follows that the shape of the issuing briquettes is determined by the shape and positioning of the pockets 21,22.

The individual pockets 21,22 are arranged so that a pocket 21 overlaps the corners ofa pair of pockets 22, as the pockets of one roll come into contact with the pockets of the other. Thus, in producing series of briquettes of alternating-D cross section, a pocket 21, overlaps, or will overlap, in part both of pockets 22,, 22,, a pocket 21, overlaps in part with both of pockets 22,, 22 and a pocket 21;,overlaps, or will have overlapped, in part both of pockets 22 22, and so on ad infinitum, as the rolls 11,12 are rotated. The overlapping thus produces both areas of overlap and areas of nonoverlap. It has been found that the areas or edges of overlap in the series of briquettes are less compacted, and therefore less dense, than webs formed in conventional operations wherein webbed spaces are maintained between briquettes.

The pockets of D-shaped cross section are so arranged that the ends of the individual briquettes, upon discharge from the rolls 11,12, are pulled in alternately one direction and thence in the other. The direction of these alternately applied forces, as shown by the smaller arrows, tend to pull individual briquettes from the pockets 21,22 upon emergence. Release is thus assisted. String breaking is also aided by the alternating directions of pull. For these reasons it has been found that series of D-shaped briquettes are readily severed through the overlapped edges or segments. The break is in a narrow plane, the direction of which is transverse to that of the issuing series.

An analysis of conditions and forces at the time of briquette formation, and in the resultant product at the locations of overlap, is belived to explain these marked improvements. The partial overlap between the pockets relieves the excessive pressure conventionally generated at the pinched edges. This results in less dense compaction, this producing less cohesion of the individual particles, and consequently less mechanical strength at an overlap (Dim. A).

In addition to these advantages, roll wear is reduce. Moreover, indexing of the rolls is less critical and there is increased throughput for a fixed roll diameter as contrasted with one containing a fixed number of pockets of similar shape.

In an improved briquetting roll design the edges of the mold segments, between the voids or pockets of the pair of rolls, as shown by reference to FIG. 4, is provided with a raised surface 23,24viz., 23, to 23,, and 24, to 24,,--which extends into a void or pocket on the opposite roll, as it revolves into position. A projection or protrusion 23,24 ranges generally from about /4 to about A as high as the pockets are deep. Also, the protrusion ranges from about V4 to about V2 as wide as the pockets, and from about $6 to about Va as long. Preferably, the protrusion is symmetrical in shape to the concave pocket in the opposite roll and in operation to two rolls are aligned so that the protrusion projects approximately into the center of the concave pocket of the opposite roll. The precise shape and location of the protrusion may be altered, but the effect is to improve the release of the molded briquettes from the rolls. The protrusions break bridges normally set up when pressing or molding the solids into shapes of concave cross section, thus giving a denser and faster melting briquette, especially when deep pockets are used. This also gives improved throughput without the problems associated with pillow briquettes. In addition, the grab characteristics of the pair of rolls is improved.

It is immaterial, in principle, whether the partial overlap is in longitudinal or transverse direction. Likewise, the overlap can be at the corners of briquettes produced by mold segments so arranged on the rolls to produce such an effect. Conventionally, however, the overlap is in the longitudinal direction along a whole edge, and in such configuration a conventional string breaker readily produces severance of the issuing series of briquettes.

In actual operation, particulate reduced iron powder percent metallized) from a fluidized iron ore reduction process, at l300 F., was subjected to a roll force of tons to produce series of alternating briquettes of D-shaped cross section, as described by reference to the preceding figures. Overlap between the individual briquettes was 13 percent. The resultant briquettes were readily released from the mold pockets using only a minimum of lubricant, and string breaking was quite effective.

A porosity of 15 percent (internal void volume relative to total volume) was achieved whereas under similar conditions pillow-shaped briquettes of 25 percent porosity were produced. The production rate in producing the D-shaped briquettes was 90 weight percent as great as in producing the pillow-shaped briquettes despite the greatly reduced porosity of the D-shaped briquettes.

It is apparent that various modifications and changes can be made without departing the spirit and scope of the present invention.

Until now the breaking of briquette strings has been a serious problem. This is particularly true with low porosity briquettes and briquettes having a relatively thick web between the briquettes. The thicker the web the harder it is to break the string. Conversely, mold wear is greater when the web is made thinner to ease the string breaking problem.

String breaking is not a problem when using the present alternating "D"-type rolls. Any slight interruption of the string flow causes the briquettes to separate. Increase in overlap thickness increases throughput and decreases roll wear along with the elimination of the web between the briquettes. The string of briquettes are readily broken into individual briquettes. This ease of string breaking is not affected even when the thickness of the overlap is quite high. The thickness of the overlap, however, aids greatly in reducing roll wear.

Having described the invention, What I claim is:

1. In roll press apparatus for serially compressing particulate metal into briquettes wherein is included a pair of cooperating rolls, one face of which is in operative association with the other, mounted for rotation in opposite directions about their respective axes,

a plurality of circumferentially uniformly spaced mold pockets located in the face of each ofthe rolls,

drive means for rotating the rolls,

and feed means for charging the particulate metal into the nip of the pair of rolls,

the improvement comprising providing a series of mold pockets in each of the rolls, said mold pockets being uniformly spaced apart, one from the other, around the roll circumference so that on rotation of said pair of cooperating rolls, roll pockets of one roll partially overlap pairs of pockets on the opposite roll in the longitudinal direction of a roll, said overlap ranging from about 1 to about 20 percent of the total longitude of the overlapped and nonoverlapped segments.

2. The apparatus of claim 1 wherein the overlap ranges from about 5 to about 15 percent.

3. The apparatus of claim 1 wherein the edges of the rolls, between the separated mold pockets, are provided with projecting surfaces which extend into the pockets of the opposite roll as the rolls are rotated.

4. The apparatus of claim 3 wherein the projections range in 

2. The apparatus of claim 1 wherein the overlap ranges from about 5 to about 15 percent.
 3. The apparatus of claim 1 wherein the edges of the rolls, between the separated mold pockets, are provided with projecting surfaces which extend into the pockets of the opposite roll as the rolls are rotated.
 4. The apparatus of claim 3 wherein the projections range in height from about one-fourth to about one-half as high as the pockets of the opposite roll are deep, as wide as from about one-fourth to about one-half as wide as said pockets, and from about three-fourths to about seven-eights as long. 